Field of the Invention
The present invention relates to optical frequency-domain reflectometry and more specifically to incoherent optical frequency domain reflectometry.
Related Art
Optical frequency-domain reflectometry (OFDR) is a popular technique for high-resolution fault allocation,1 optical fiber component characterization,1,2,3,4 and distributed temperature and strain sensing.5 In coherent optical frequency domain reflectometry (C-OFDR) a tunable laser and an interferometer are utilized for superposing a swept-laser signal with a time-delayed version of the same signal in order to generate a beat signal1. Spectral analysis of the beat signal allows for the determination of the locations of reflection points along a laser path at high spatial-resolution and high dynamic-range.1,2,6 The utilization of an interferometer makes C-OFDR highly dependent on the laser coherence properties, thus limiting the reflection detection range.1 
Several approaches have been used for range extension in C-OFDR. Utilization of a highly coherent swept-laser implemented using a narrow linewidth fiber laser and a piezoelectric tuner has, for example, allowed for the reflection point locations as far as 95 km up along a length of fiber to be detected at an unspecified spatial-resolution.7 Phase-noise-compensation has allowed for the location of reflection points as far as 80 km to be determined at a spatial-resolution of 20 cm.8 Band-width division has been combined with phase-noise-compensation to locate reflections as far as 40 km at an improved spatial-resolution of 5 cm.9 Most recently, phase-noise measurements for a swept-laser reflected from points beyond the laser coherence length has allowed for the location of Fresnel reflections, as far as 170 km, to be detected at a spatial resolution of 200 m.10 
Incoherent optical frequency domain reflectometry (I-OFDR) has been investigated as an alternative for C-OFDR as it does not depend on the coherence length of the laser signal and therefore it intrinsically allows for long-range reflection measurements.11,12,13 In I-OFDR, the acquisition and spectral analysis of a beat signal between a frequency-swept sinusoidal optical signal and a time-delayed version of the same signal determines the location of reflection points along the signal path. Existing implementations of I-OFDR utilize optoelectronic components and electronic signal processors for beat acquisition. The bandwidth cap of electronic and optoelectronic devices limit the maximum sweep frequency-span and therefore the minimum spatial-resolution achievable with conventional I-OFDR.